Time-dependent fracture of cementitious materials

The response of cementitious materials is highly time dependent. On the one hand, it can lead to delayed collapse of structures fabricated of such materials. On the other hand, the time dependence is associated with the relaxation of peak stresses, which avoids, or postpones damage. A finite element formulation is presented for the analysis of...

A comparison between ultra-high-strength and conventional high-strength fastener steels: Mechanical properties at elevated temperature and microstructural mechanisms

A comparison is made between the mechanical properties of the ultra-high-strength steel KNDS4 of fastener grade 14.9 and of conventional, high-strength steels 34Cr4 of fastener grade 12.9 and 33B2 of grade 10.9. The results show that the ratio of the yield strength at elevated temperatures to the yield strength at room temperature is higher for...

Finite element modelling of creep cavity filling by solute diffusion

In recently discovered self healing creep steels, open-volume creep cavities are filled by the precipitation of supersaturated solute. These creep cavities form on the grain boundaries oriented perpendicular to the applied stress. The presence of a free surface triggers a flux of solute from the matrix, over the grain boundaries towards the...

Predictive potential of Perzyna viscoplastic modelling for granular geomaterials

This paper reappraises Perzyna-type viscoplasticity for the constitutive modelling of granular geomaterials, with emphasis on the simulation of rate/time effects of different magnitude. An existing elasto-plastic model for sands is first recast into a Perzyna viscoplastic formulation and then calibrated/validated against laboratory test...

Effect of experimental conditions on nano-indentation response of low density polyethylene (LDPE)

Nano-indentation is an interesting tool for analyzing nano-scale mechanical properties. The analysis of nano-mechanical properties as a function of experimental conditions is very critical for designing engineering components. In this study, nano-indentation experiments were performed by considering different values of amplitude (1, 5, 10 nm...

Creep failure of reformer tubes in a petrochemical plant

This paper investigates a failure in HP-Mod radiant tubes in a petrochemical plant. Tubes fail after 90,000 h of working at 950 °C. Observed failure is in the form of excessive bulging and longitudinal cracking in reformer tubes. Cracks are also largely branched. The microstructure of service-exposed tubes was evaluated using optical and...

Failure Analysis of Two HP-Nb Heat-Resistant Tubes after 46,000 h Exposure to Reformer Service Conditions

This study presents a failure analysis in two reformer tubes used for hydrogen production in a petrochemical industry. These tubes (Tube A and Tube B) were made by the centrifugal casting of HP-Nb alloy in such a way that one contained titanium as a micro-element, and the other was free from titanium in its chemical composition. Although the two...

Modelling the time-dependent mechanical behaviour of clay rocks based on meso- and micro-structural viscous properties

Clay rocks are multiphase porous media having a complex structure and behaviour characterised by heterogeneity, damage and viscosity, existing on a wide range of scales. The mesoscopic scale of mineral inclusions embedded in a clay matrix has an important role in the mechanisms of deformation under mechanical loading by cracking and creeping....